M.Sc. / Several characteristics of the homothallic species, Chaetomium aureum, c erraticum, c flavigenum, c rubrogenum and c trilaterale, were examined and compared. Morphological details such as perithecial structure, form and ornamentation of the setae and spores, physiological aspects such as formation of pigment and cellulolytic activity as well as nuclear behaviour during ascosporogenesis were examined to determine their species differentiating potential. Although pigment formation and ornamentation of setae are environment dependent these features could be useful in species delimitation ...

No description available.

Ganoderma lucidum and G. tsugae are two members of the G. lucidum complex. The authenticity of the two wood-rotting species was demonstrated by comparative studies. Ganoderma lucidum is restricted to hardwoods. Its "smooth" walled basidiospores were characterized by narrow, numerous inter-wall pillars. Isolates of G. lucidum produced chlamydospores in culture and had an average growth of 7.8 mm/da at their optimum temperature range of 30-34 C. Ganoderma tsugae is restricted to conifers. Its basidiospores were "rough" walled and had broad inter-wall pillars. Isolates of G. tsugae did not produce chlamydospores in culture and had an average growth of 2.1 mm/da at the optimum temperature range of 20-25 C. Mating systems were determined for both species as heterothallic and tetrapolar. Interspecific matings of homokaryons were incompatible. Homokaryons of a European G. resinaceum isolate were interfertile with homokaryons from North American collections of G. lucidum. The ability of G. lucidum and G. tsugae to decay wood in vitro was studied using the following woods in agar block decay chambers: grape, oak, mesquite, white fir, and Douglas-fir. Grape wood lost the most weight while mesquite the least. G. lucidum isolates generally caused greater weight loss of all woods than did G. tsugae isolates. Both Ganoderma species caused simultaneous decay in all woods. However, chemical analyses of the decayed blocks indicated that selective delignification by both species also occurred in grape and white fir blocks but not in oak or Douglas-fir blocks. Scanning electron microscopy demonstrated various stages of selective delignification and simultaneous decay of all woods tested. Isolates of Ganoderma lucidum infected Dog Ridge variety grape plants, grown in the greenhouse, from below-ground wood block inoculations. Twenty-four plants were inoculated: one plant died and 4 other plants declined. After 24 months reisolations yielded only G. lucidum from the five declining plants, demonstrating pathogenicity. The fungus developed in the heartwood and, in later stages, invaded the sapwood. Infected plants developed water stress symptoms with leaves wilting, yellowing, and dying. Field grape plants inoculated with the fungus developed decay columns as large as 42 cm in 17 mons. Decay was limited to the heartwood; no foliar symptoms occurred.

No description available.

M.Sc. (Botany) / The genus Phomopsis is an important fungal genus due to its widespread pathogenicity on a wide variety of hosts and its complex anamorphic morphology. Three species of the genus Phomopsis viz. Phomopsis citri, Phomopsis leptostromiformis and Phomopsis zeicola, were studied in artificial culture and on host plants in vitro. The culture of Phomopsis citri failed to form conidiomata in culture and this species was studied intensively. As the species in this genus are difficult to distinguish and identify, the species named above were compared in an attempt to define taxonomically usable distinguishing characters. The morphology and ontogeny of the colonies, conidiomata and conidia, the karyology of these species, pathogenicity to cultivars of Lupinus spp. and Zea mays, were studied and the pectic enzymes were analyzed. Optical-, scanning electron- and transmission electron microscopic techniques were used in addition to the enzyme analysis. The conidiomata were typically stromatic and often irregularly multiloculate and could arise from more than one type of primordium. The most common primordia were ringshaped structures but hyphal aggregations were also found. Conidiogenesis was phialidic and the a-conidia of both species examined were shown to be uninucleate. The {3-conidia of Phomopsis leptrostromiformis were similarly uninucleate but failed to germinate. Their function is thus still unknown. Phomopsis zeicola failed to form {3-conidia. Transmission electron microscopy showed differences in conidial morphology between these species which, together with pectic enzyme analysis, could be good characters to separate species in this genus. The implications of heterokaryosis are discussed in assessing the potential value of these parameters and further investigations will have to be done.

The consequences of toxigenic fungi associated with stored seed have stimulated these investigations aimed at developing treatments to minimise this mycoflora, without significantly reducing seed quality or viability. The effects of immersion in water at 55, 57 and 60 QC for durations of 5 to 60 min were assessed for maize (Zea mays L.) seed in terms of fungal status, water uptake, electrolyte leakage, germination and seedling establishment. These assessments were conducted immediately after treatment, after re-dehydration for 2 days in an ambient air stream, and following a 1 month storage period under either cold (4 QC) or ambient (25 QC) conditions (33% and 91% RH, respectively). In all cases, the results are compared with those of control seeds and seeds pre-imbibed for 4 h at ambient temperature. The level of internal contamination, represented almost entirely by Fusarium moniliforme Sheldon, declined significantly when assessed immediately after treatment, the efficacy of which increased with increasing temperature and duration of treatment. Seeds immersed in water at 55 QC for a duration of 15 min exhibited an 85% reduction in infection levels, when compared with those of the control, while those treated at 57 and 60 QC (same duration) were uninfected. Immersing seeds in hot water, however, resulted in a lag in germination rate and drop in germination totality, the degree of which was enhanced by increasing duration and temperature of treatment, suggesting the status of the manipulation to be an accelerated ageing treatment. The electrolyte leakage studies indicated that the reduced germination performance of these seeds was not due to plasmalemma disorganisation. These deleterious effects, however, were counter-balanced as seeds treated at 55, 57 and 60 QC for durations up to 60, 30 and 10 min, respectively, produced plants of superior quality than those of the control, which is ascribed to the reduction of systemically transmitted pathogens. The efficacy of the hot water treatment in reducing the levels of seed infection and improving seedling quality was enhanced by subsequent re-dehydration. The reduction in seed-associated mycoflora was maintained following storage for 1 month at both 4 QC (33% RH) and 25 QC (91% RH). However, both seed and seedling quality were adversely affected following storage even under cold, dry conditions, which may be a consequence of the pre-treatment history of the seeds, which had been cold-stored for two years prior to the experiments. Applied as a pre-sowing treatment, therefore, hot water treatment shows promise for producing a crop of superior quality, less prone to fusarial pathogenesis. This treatment may be of particular importance to Third-World subsistence communities. / Thesis (M.Sc.)-University of Natal, 1995.

Thesis (MScAgric)--Stellenbosch University, 1948. / NO ABSTRACT AVAILABLE